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Six essential steps before fabric dyeing and finishing

Update:21 Apr 2020
Summary:

Abstract: Fabric dyeing and finishing is an important p […]

Abstract: Fabric dyeing and finishing is an important part of fabrics. Any slight mistakes may cause fabric dyeing and finishing failure, which will cause defects in the entire batch of fabrics, affecting quality and price. The following six steps will explain the details of the fabric before dyeing and finishing. ⑴Gray cloth preparation: There are three main points for the preparation of gray cloth: gray cloth inspection-turning over cloth (batch, box, printing)-seam head. ⑵ Singeing: The fluff on the surface of the fabric will affect the quality and performance of the dyeing and finishing process, and must be singed

Key words:

Dyeing and finishing of fabrics is an important part of fabrics. Any minor mistakes may cause the failure of dyeing and finishing of fabrics, causing defects in the entire batch of fabrics, affecting quality and price. The following six steps will explain the details of the fabric before dyeing and finishing.

 

⑴Gray cloth preparation: There are three main points for the preparation of gray cloth: gray cloth inspection-turning over cloth (batch, box, printing)-seam head.

⑵ Singeing: The fluff on the surface of the fabric will affect the quality and consumption performance of the dyeing and finishing process, and it must undergo singeing treatment to make the cloth smooth and clean. Singeing is to make the grey cloth quickly pass the flame of the singeing machine or wipe the red hot metal surface in a flat form, causing the fluff on the fabric to burn due to rapid temperature rise, while the fabric itself is relatively compact, thick, and relatively warm. Slow, when the temperature has not reached the ignition point, it has left the flame or the red hot metal surface, so as to achieve the purpose of burning away the fluff without damaging the fabric.

⑶ Desizing: Before weaving, the warp yarns are generally sizing treated to improve the strength, wear resistance and smoothness of the warp yarns, which is convenient for weaving. However, the slurry on the grey fabric is not good for printing and dyeing, because the presence of the slurry will contaminate the entire working fluid, consume dye and chemical materials, and even hinder the dyeing of the raw materials and affect the quality of printing and dyeing products. Therefore, the fabric must be desizing at the beginning of the dyeing and finishing process.
Desizing can be divided into enzyme desizing, alkaline desizing, acid desizing and oxidant desizing. The desizing alkali is currently the most common method used by printing and dyeing plants. It is used on pure cotton or blended fabrics and can remove most of the slurry. It also has a certain decomposition and removal of natural impurities on cotton fibers, but because alkali desizing only reduces the adhesion of the slurry to the fabric and does not degrade the slurry, it must be fully washed after desizing and the washing liquid must be continuously replaced . Because desizing caustic soda is generally waste alkali, desizing cost is lower.

⑷Smelting: After the desizing of cotton fiber fabrics, most of the slurry and a small part of natural impurities have been removed, but most of the natural impurities in cotton fibers, such as waxy substances, pectin, nitrogen-containing substances, cotton seed hulls A small amount of oil agent and a small amount of slurry remain on the fabric, making the cotton fiber fabric yellowish and poor in moisture absorption and permeability, which cannot meet the requirements of subsequent dyeing and finishing processes. In order to make the cotton fiber fabric have a certain degree of water absorption and permeability, it is conducive to the absorption and diffusion of dye additives during the dyeing and finishing process, so after desizing, it must be cooked to remove most of the residual impurities in the cotton fiber .

⑸ Bleaching: After scouring, most impurities have been removed and the water absorption has been greatly improved. However, due to the presence of natural pigments on the fiber, the appearance is not white enough. Except for a few varieties, generally Bleaching, otherwise it will affect the vividness of dyeing or printing. The purpose of bleaching is to destroy natural pigments and ensure the necessary and stable whiteness of the fabric while ensuring that the fibers are not significantly damaged, while removing impurities (especially cottonseed hulls) that remain after cooking. The bleaching agents currently used in cotton fiber fabrics are sodium hypochlorite, hydrogen peroxide (commonly known as hydrogen peroxide) and sodium chlorite. Each of these three bleaches has its own characteristics and uses.

⑹ Mercerization: Mercerization refers to the fabric containing cotton fiber undergoing concentrated caustic soda treatment under a certain tension and maintaining the required size. As a result, the fabric obtains silk-like gloss. In addition, the strength and elongation of the fabric And the size and morphological stability have also been improved, the chemical reaction capacity of the fiber and the adsorption capacity of the dye have also been improved, so mercerizing of fiber-containing fabrics is one of the important tasks of dyeing and finishing.


The main factors affecting the mercerizing effect are the concentration of alkali solution, temperature, action time and the tension applied to the fabric. The most commonly used method for testing mercerizing effect is the barium value method for measuring the adsorption capacity of cotton fiber to chemicals. The higher the barium value, the better the mercerizing effect. Generally, the barium value of this smooth cotton fiber fabric is 100. The barium value of the mercerized thick fabric is often between 130 and 150, and the barium value above 150 indicates that the cotton fiber is sufficiently mercerized.
 
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